Heat-peelable pressure-sensitive adhesive sheet and method for processing adherend using the heat-peelable pressure-sensitive adhesive sheet

ABSTRACT

Disclosed is a heat-peelable pressure-sensitive adhesive sheet that can prevent the deformation of a pressure-sensitive adhesive layer caused by pressurization, further reduce chipping in grinding and cutting processes, be easily peeled off from a processed article after processing, and can be easily applied to an adhered at ordinary temperature. The heat-peelable pressure-sensitive adhesive sheet includes a substrate, and a heat-expandable pressure-sensitive adhesive layer arranged on or above at least one side of the substrate, the heat-expandable pressure-sensitive adhesive layer containing a foaming agent and having a shear modulus (23° C.) in an unfoamed state of 7×10 6  Pa or more. The adhesive sheet further includes a pressure-sensitive adhesive layer being arranged on or above heat-expandable pressure-sensitive adhesive layer, wherein the pressure-sensitive adhesive layer has a shear modulus (23° C.) of less than 7×10 6  Pa and a thickness of 0.01 to 10 μm.

TECHNICAL FIELD

The present invention relates typically to heat-peelablepressure-sensitive adhesive sheets and methods for processing anadherend using the heat-peelable pressure-sensitive adhesive sheets.

BACKGROUND ART

Demands have been recently made on electronic components to have reducedsizes and increased precise. Ceramic capacitors, for example, must havereduced sizes such as “0603” size and “0402” size and have largercapacities as a result of high integration of layers in a numberexceeding several hundreds. In particular, satisfactory processingaccuracy has been required to realize size reduction and precisionincrease in laminating of ceramic sheets before firing (ceramic greensheets) typically for constituting ceramic capacitors.

Taking a method for producing a ceramic capacitor as an example, itincludes, for example, the steps (processes) of (1) printing electrodesto green sheets, (2) laminating the printed green sheets, (3) pressing(pressing under pressure), (4) cutting, and (5) firing, in which thecutting process (4) is conducted after repeating the laminating process(2) and the pressing process (3) predetermined times.

Required precisions (accuracies) on these processes include theprecision of printing electrodes in the process (1) of printingelectrodes to green sheets; the precision of aligning electrodes in thelaminating process (2); the precision of preventing misregistration ofelectrodes due to deformation of the green sheets as a result ofpressurization in the pressing process (3); and the precision of cuttingin the cutting process (4). Products become defective and have decreasedproductivity even when only one of these precisions is low in theseprocesses.

Of these, the precisions required in the process (1) of printingelectrodes to green sheets, the laminating process (2), and the cuttingprocess (4) are mechanical precisions, and they can be achieved byrealizing improvements in apparatuses and in precision. In the pressingprocess (3), however, the green sheets may deform and undergomisregistration as a result of pressurization (pressing under pressure),and this may cause the misregistration of electrodes and affect theprecision of electrode registration in the green sheets laminated in thelaminating process (2).

In current laminating processes (2), green sheets are generallylaminated on poly(ethylene terephthalate) films (PET films) orpressure-sensitive adhesive tapes. Among them, the lamination of greensheets on pressure-sensitive adhesive tapes is increasingly employedfrom the viewpoints of size reduction and satisfactory anchoring(fixing) of green sheets in the subsequent cutting process.

Pressure-sensitive adhesive tapes used herein are adhesive tapes thatexhibit tackiness (pressure-sensitive adhesion) at ordinary temperatureso as to adhere to (fix) green sheets during the laminating process,pressing process, and cutting process, and have decreased tackiness as aresult typically of heating or irradiation with ultraviolet rays, andcan be peeled off after the cutting process. Examples of such adhesivetapes are heat-peelable pressure-sensitive adhesive sheets eachincluding a substrate and a heat-expandable pressure-sensitive adhesivelayer arranged at least on one side of the substrate; ultravioletcurable/peelable pressure-sensitive adhesive sheets; and low-tackadhesive tapes, as disclosed typically in Japanese Examined PatentApplication Publication (JP-B) No. Sho 50-13878, JP-B No. Sho 51-24534,Japanese Unexamined Patent Application Publication (JP-A) No. Sho56-61468, JP-A No. Sho 56-61469, and JP-A No. Sho 60-252681. Morespecifically, taking heat-peelable pressure-sensitive adhesive sheets asan example, they show both adhesiveness before heating and peelabilityafter heating. Namely, after achieving the target adhesion,heat-expandable microspheres in the heat-expandable pressure-sensitiveadhesive layer are heated to foam or expand, and the surface of theheat-expandable pressure-sensitive adhesive layer becomes uneven. Thisreduces the adhesion area (contact area) with an adherend (work) tothereby reduce the adhesive strength. Thus, the adherend can be easilypeeled off (separated) from the adhesive tapes.

Such processes using pressure-sensitive adhesive tapes are generallyused in production processes such as dicing and back grinding in theproduction of semiconductor components, some of which are expanded touse heat-peelable pressure-sensitive adhesive sheets.

DISCLOSURE OF INVENTION

However, a pressure-sensitive adhesive tape, if used in the productionof ceramic capacitors having a reduced size and/or higher precision asmentioned above, may deform in its pressure-sensitive adhesive layerupon pressurization in the pressing process, which may cause deformationand thereby invite poor precision in the electrode registration.Materials having a high elastic modulus at ordinary temperature, such asPET films, are relatively resistant to such misregistration caused bypressurization.

It has been revealed that pressure-sensitive adhesive tapes preferablyhave a small thickness of adhesive (thickness of the pressure-sensitiveadhesive layer) and a high elastic modulus so as to minimize chipping ingrinding and cutting processes, such as dicing process, in theproduction processes of semiconductor components. However, heat-peelablepressure-sensitive adhesive sheets, if used as the pressure-sensitiveadhesive tapes, are difficult to have a small thickness in thepressure-sensitive adhesive layer (heat-expandable pressure-sensitiveadhesive layer), because the pressure-sensitive adhesive layer containsheat-expandable microspheres. A possible solution to reduce chipping inthese adhesive sheets, therefore, is increase in elastic modulus of thepressure-sensitive adhesive layer.

Thus, heat-peelable pressure-sensitive adhesive sheets for use inelectronic components and semiconductor components may possibly be thosehaving a high elastic modulus of a pressure-sensitive adhesiveconstituting the heat-expandable pressure-sensitive adhesive layer.Accordingly, the present inventors prepared a heat-peelablepressure-sensitive adhesive sheet containing a substrate, and aheat-expandable pressure-sensitive adhesive layer arranged on or aboveat least one side of the substrate, which heat-expandablepressure-sensitive adhesive layer includes heat-expandable microspheresand has a shear modulus (23° C.) in an unfoamed state of 7×10⁶ Pa ormore. The heat-peelable pressure-sensitive adhesive sheet preventsdeformation during pressing under pressure in the production ofelectronic components and prevents chipping to thereby realize reducedchipping in the production of semiconductor components. The adhesivesheet can have a reduced shear modulus of less than 7×10⁶ Pa to therebyexhibit tackiness when heated at temperatures equal to or lower thanfoam initiating temperature of the heat-expandable microspheres in theheat-expandable pressure-sensitive adhesive layer. Thus, the adhesivesheet can act to adhere to (fix) the adherend in laminating in theproduction of electronic components and in cutting in the production ofsemiconductor components. In addition, the heat-peelablepressure-sensitive adhesive sheet can be easily peeled off from theadherend after the use thereof (for example, after the cutting processin the production of electronic components and after the dicing processin the production of semiconductor components) by heating totemperatures equal to or higher than the foam initiating temperature ofthe heat-expandable microspheres in the heat-expandablepressure-sensitive adhesive layer. This is because the heat-expandablemicrospheres in the heat-expandable pressure-sensitive adhesive layerfoam or expand at such temperatures to thereby significantly reduce thetackiness.

The heat-peelable pressure-sensitive adhesive sheet of this type,however, is poor in tack of the heat-expandable pressure-sensitiveadhesive layer and is thereby poor in adhesion at ordinary temperature,because the heat-expandable pressure-sensitive adhesive layer has ashear modulus at ordinary temperature (23° C.) in an unfoamed state of7×10⁶ Pa or more.

Accordingly, an object of the present invention is to provide aheat-peelable pressure-sensitive adhesive sheet, even if used in theproduction of electronic components and semiconductor components, whichcan prevent deformation of the pressure-sensitive adhesive layer as aresult of pressurization during the pressing process and exhibitexcellent tackiness so as to prevent misregistration of adherends duringthe laminating and cutting processes in the production of electroniccomponents. The adhesive sheet can also exhibit excellent tackiness andrealize further reduced chipping during the grinding and cuttingprocesses in the production of semiconductor components and can bepeeled off from an adherend (processed article) after the processing. Inaddition, the adhesive sheet, if used as a pressure-sensitive adhesivetape, can easily adhere to an adhered at ordinary temperature. Anotherobject of the present invention is to provide a method for processing anadherend using the heat-peelable pressure-sensitive adhesive sheet.

Yet another object of the present invention is to provide aheat-peelable pressure-sensitive adhesive sheet that can contribute toimprovement in component precision, reduction in size of the adherend,and improvement in yield to thereby effectively improve theproductivity. Still another object of the present invention is toprovide a method for processing an adherend using the heat-peelablepressure-sensitive adhesive sheet.

After intensive investigations to achieve the objects, the presentinventors have found that a heat-peelable pressure-sensitive adhesivesheet having a specific layer configuration and including aheat-expandable pressure-sensitive adhesive layer having specificproperties can achieve the objects, if used as a pressure-sensitiveadhesive tape in the production of electronic components andsemiconductor components. Specifically, the heat-peelablepressure-sensitive adhesive sheet can easily adhere to an adherend evenat ordinary temperature, prevent deformation as a result of pressingunder pressure in the production of electronic components, and realizefurther reduced chipping during dicing in the production ofsemiconductor components. The adhesive sheet can be easily peeled offfrom the processed article after processing. In addition, they havefound that the heat-peelable pressure-sensitive adhesive sheet can alsohave such a configuration as to exhibit excellent tackiness in thelaminating or cutting process in the production of electroniccomponents. The present invention has been achieved based on thesefindings.

Specifically, the present invention provides a heat-peelablepressure-sensitive adhesive sheet comprising a substrate; and aheat-expandable pressure-sensitive adhesive layer arranged on or aboveat least one side of the substrate, the heat-expandablepressure-sensitive adhesive layer containing a foaming agent and havinga shear modulus (23° C.) in an unfoamed state of 7×10⁶ Pa or more, inwhich the adhesive sheet further comprises a pressure-sensitive adhesivelayer being arranged on or above the heat-expandable pressure-sensitiveadhesive layer and having a shear modulus (23° C.) of less than 7×10⁶Pa. The heat-expandable pressure-sensitive adhesive layer preferablycomprises a pressure-sensitive adhesive having a shear modulus (23° C.)after being cured or dried of 7×10⁶ Pa or more, and thepressure-sensitive adhesive layer arranged on or above theheat-expandable pressure-sensitive adhesive layer preferably comprises apressure-sensitive adhesive having a shear modulus (23° C.) after beingcured or dried of less than 7×10⁶ Pa. The pressure-sensitive adhesivelayer arranged on or above the heat-expandable pressure-sensitiveadhesive layer has a thickness of 0.01 to 10 μm. The heat-expandablepressure-sensitive adhesive layer is preferably arranged above thesubstrate with the interposition of an organic rubber-like elasticlayer.

The heat-expandable pressure-sensitive adhesive layer in theheat-peelable pressure-sensitive adhesive sheet can have a shear modulus(95° C.) in an unfoamed state of less than 7×10⁶ Pa. The foaming agentin the heat-expandable pressure-sensitive adhesive layer preferably hasa foam initiating temperature higher than 80° C.

The present invention further provides a method of processing anadherend, comprising the steps of applying the heat-peelablepressure-sensitive adhesive sheet to the adherend, and subjecting theadherend to processing. The adherend is preferably an article to be anelectronic component and an article to be a semiconductor component.

The present invention still further provides an electronic component anda semiconductor component produced using the method of processing anadherend.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a part of a heat-peelablepressure-sensitive adhesive sheet as an embodiment of the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

Certain embodiments of the present invention will be illustrated indetail below, with reference to the attached drawing according tonecessity. Identical members and sections may have identical referencenumerals.

[Heat-Peelable Pressure-Sensitive Adhesive Sheet]

The heat-peelable pressure-sensitive adhesive sheets according to thepresent invention have a configuration comprising a substrate, aheat-expandable pressure-sensitive adhesive layer, and apressure-sensitive adhesive layer arranged in this order. Theheat-expandable pressure-sensitive adhesive layer comprisesheat-expandable microspheres as a foaming agent and has a shear modulus(23° C.) in an unfoamed state of 7×10⁶ Pa or more. Thepressure-sensitive adhesive layer arranged on or above theheat-expandable pressure-sensitive adhesive layer has a shear modulus(23° C.) of less than 7×10⁵ Pa. These heat-peelable pressure-sensitiveadhesive sheets include, for example, a pressure-sensitive adhesivesheet having the configuration shown in FIG. 1. FIG. 1 is a schematiccross-sectional view of a part of a heat-peelable pressure-sensitiveadhesive sheet as an embodiment of the present invention. FIG. 1illustrates a heat-peelable pressure-sensitive adhesive sheet 1, asubstrate 2, an organic rubber-like elastic layer 3, a heat-expandablepressure-sensitive adhesive layer 4, a pressure-sensitive adhesive layer5, and a separator (release liner) 6. The heat-expandablepressure-sensitive adhesive layer 4 has a shear modulus (23° C.) in anunfoamed state of 7×10⁶ Pa or more, and the pressure-sensitive adhesivelayer 5 has a shear modulus (23° C.) of less than 7×10⁶ Pa.

Specifically, the heat-peelable pressure-sensitive adhesive sheet 1 inFIG. 1 comprises the substrate 2; the organic rubber-like elastic layer3 arranged on or above one side of the substrate 2; the heat-expandablepressure-sensitive adhesive layer 4 arranged on the organic rubber-likeelastic layer 3; and the pressure-sensitive adhesive layer 5 arranged onthe heat-expandable pressure-sensitive adhesive layer 4, in which thepressure-sensitive adhesive layer 5 is protected by the separator 6. Theheat-expandable pressure-sensitive adhesive layer 4 has a shear modulus(23° C.) in an unfoamed state of 7×10⁶ Pa or more, and thepressure-sensitive adhesive layer 5 has a shear modulus (23° C.) of lessthan 7×10⁶ Pa. The organic rubber-like elastic layer 3 can be optionallyarranged.

The heat-peelable pressure-sensitive adhesive sheets according to thepresent invention each comprise the heat-expandable pressure-sensitiveadhesive layer having a shear modulus (23° C.) in an unfoamed state of7×10⁶ Pa or more and the pressure-sensitive adhesive layer beingarranged on or above the heat-expandable pressure-sensitive adhesivelayer and having a shear modulus (23° C.) of less than 7×10⁶ Pa.Accordingly, they exhibit elasticity and excellent adhesiveness. Whenthey are used, for example, in the pressing process (pressing underpressure), laminating process, and cutting process in the production ofelectronic components, they can prevent the deformation of theheat-expandable pressure-sensitive adhesive layer upon pressurizationand inhibit the misregistration of the adherend during laminating andcutting by carrying out the pressurization (pressing under pressure),laminating, and cutting at room temperature. When they are used in thegrinding process, such as a back grinding process, and the cuttingprocess, such as a dicing process, in the production of semiconductorcomponents, they can prevent the chipping by carrying out back grindingand dicing at room temperature. The chipping herein refers to damages ofcomponents such as articles to be a semiconductor component, includingsilicon wafers, and articles to be an electronic component. Theheat-peelable pressure-sensitive adhesive sheets according to thepresent invention, if used in adherend processing, can moresatisfactorily prevent the deformation of the heat-expandablepressure-sensitive adhesive layer during pressing process in theproduction of electronic components and can more satisfactorily preventthe misregistration of the adherend during laminating and cuttingprocesses in the production of electronic components. They can alsorealize further reduced chipping (or further prevented chipping) duringgrinding and cutting processes in the production of semiconductorcomponents.

The heat-peelable pressure-sensitive adhesive sheets, when used inprocessing of an adherend, such as an article to be an electroniccomponent or an article to be a semiconductor component, can improve theprecision of the processed article or component, enable the article orcomponent to have reduced size, improve yields, and thereby improve theproductivity.

The heat-expandable pressure-sensitive adhesive layer preferably has ashear modulus (23° C.) in an unfoamed state of 7×10⁶ Pa or more and ashear modulus (80° C.) in an unfoamed state of less than 7×10⁶ Pa, andmore preferably has a shear modulus (23° C.) in an unfoamed state of7×10⁶ Pa or more and a shear modulus (95° C.) in an unfoamed state ofless than 7×10⁶ Pa. By satisfying this, the adhesive sheets can adhereto the adherend more firmly by heating. It should be noted that thetemperature in heating herein must be a temperature lower than the foaminitiating temperature of the foaming agent in the heat-expandablepressure-sensitive adhesive layer. In processes requiring tackiness,such as laminating and cutting processes in the production of electroniccomponents, or grinding and cutting processes in the production ofsemiconductor components, the adhesive sheets can exhibit more firmadhesion upon laminating and cutting, or upon back grinding and dicing,by carrying out laminating and cutting, or back grinding and dicingafter once heating the adhesive sheets. It should be noted that thetemperature in heating herein must be a temperature lower than the foaminitiating temperature of the foaming agent in the heat-expandablepressure-sensitive adhesive layer. Where necessary, the adhesive sheetscan be cooled to room temperature after heating and before processing.The heat-peelable pressure-sensitive adhesive sheets, if having theseproperties, can satisfy both elasticity and adhesiveness at high levels,which elasticity is required in the pressing process in the productionof electronic components, and which adhesiveness is required in thelaminating and cutting processes in the production of electroniccomponents, and in the grinding and cutting processes in the productionof semiconductor components. The adhesive sheets can therefore furtherimprove the precision of the processed article or component, enable thearticle or component to have a further reduced size, improve yields, andthereby further increase the productivity.

The heat-peelable pressure-sensitive adhesive sheets can be easilypeeled off from the processed article, such as an electronic componentor a semiconductor component, by carrying out a heat treatment afterprocessing.

(Substrate)

The substrate can serve as a matrix for supporting the heat-expandablepressure-sensitive adhesive layer, the pressure-sensitive adhesivelayer, and other layers. The substrate can be any suitable thin articleincluding paper substrates such as paper; fibrous substrates such aswoven or nonwoven fabrics and nets; metallic substrates such as metalfoil and metal sheets; plastic substrates such as plastic films andsheets; rubber substrates such as rubber sheets; foamed articles such asfoamed sheets; and laminates of these materials. Of such laminates,laminates of a plastic substrate with another substrate, and laminatesof plastic films or sheets with each other are preferred. The substrateis preferably one that has excellent thermal stability and is not moltenat temperatures in the heat treatment of the heat-expandablepressure-sensitive adhesive layer. Such a substrate shows goodhandleability after heating. The substrate is preferably a plasticsubstrate such as a plastic film or sheet. Examples of the materials forsuch plastic films and sheets include olefinic resins comprising anα-olefin as a monomer component, such as polyethylenes (PEs),polypropylenes (PPs), ethylene-propylene copolymers, and ethylene-vinylacetate copolymers (EVAs); polyesters such as poly(ethyleneterephthalate)s (PETs), poly(ethylene naphthalate)s (PENs), andpoly(butylene terephthalate)s (PBTs); poly(vinyl chloride)s (PVCs);poly(phenylene sulfide)s (PPSs); amide resins such as polyamides(nylons) and wholly aromatic polyamides (aramids); and poly(ether etherketone)s (PEEKs). Each of these materials can be used alone or incombination.

A plastic substrate, if used as the substrate, can be controlled uponpercentage of elongation and other deformation properties typically bydrawing. When a radiation curable substance is used typically in theheat-expandable pressure-sensitive adhesive layer, the substrate ispreferably one that does not inhibit the transmission of the radiation.

The thickness of the substrate can be appropriately selected accordingto the strength, flexibility, and objected use of the substrate, and isgenerally about 1000 μm or less, for example, about 1 to about 1000 μm,preferably about 1 to about 500 μm, more preferably about 3 to about 300μm, and particularly preferably about 5 to about 250 μm. The thickness,however, is not specifically limited. The substrate can comprise asingle layer or multiple layers.

The surface of the substrate can be subjected, for example, to aconventional surface treatment and/or coating with a primer forincreasing the adhesion typically with the heat-expandablepressure-sensitive adhesive layer. Examples of the surface treatmentinclude corona treatment, chromium acid treatment, exposure to ozone,exposure to flame, exposure to high-pressure electric shock, and otherchemical or physical oxidation treatments. The surface can be coated,for example, with a release agent such as a silicone resin orfluorocarbon resin, for imparting the peelability typically from theheat-expandable pressure-sensitive adhesive layer.

The heat-expandable pressure-sensitive adhesive layer is arranged on orabove at least one side (one side or both sides) of the substrate withor without the interposition of an intermediate layer such as an organicrubber-like elastic layer. The substrate may be embedded in theheat-expandable pressure-sensitive adhesive layer.

(Heat-Expandable Pressure-Sensitive Adhesive Layer)

The heat-expandable pressure-sensitive adhesive layer has a shearmodulus (23° C.) in an unfoamed state after being cured or dried of7×10⁶ Pa or more, as is mentioned above. The shear modulus herein ispreferably 1×10⁷ Pa or more. It is preferred that the heat-expandablepressure-sensitive adhesive layer has a shear modulus (23° C.) in anunfoamed state after being cured or dried of 7×10⁶ Pa or more,preferably 1×10⁷ Pa or more, and has a shear modulus (80° C.) in anunfoamed state after being cured or dried of less than 7×10⁶ Pa,preferably 5×10⁶ Pa or less. It is more preferred that theheat-expandable pressure-sensitive adhesive layer has a shear modulus(23° C.) in an unfoamed state after being cured or dried of 7×10⁶ Pa ormore, preferably 1×10⁷ Pa or more, and has a shear modulus (95° C.) inan unfoamed state after being cured or dried of less than 7×10⁶ Pa,preferably 5×10⁶ Pa or less.

The “shear modulus” used in the present specification means a shearstorage elastic modulus. The procedure for determining the shear modulus(shear storage elastic modulus) of the heat-expandablepressure-sensitive adhesive layer can be, but not specifically limitedto, a conventional determination procedure of dynamic viscoelasticproperties. More specifically, a dynamic viscoelastometer as the productof Rheometrics Inc. under the trade name of “ARES” can be used. Thedetermination can be carried out under such conditions at temperaturesof 23° C., and 80° C. or 95° C., a frequency of 1 Hz, a sample thickness(the thickness of the heat-expandable pressure-sensitive adhesive layer)of about 1.0 mm or about 2.0 mm, and a strain of 0.1% (23° C.) or 0.3%(80° C. or 95° C.), using a jig including parallel plates having a platediameter of 7.9 mm. The higher temperature (80° C. or 95° C.) in thedetermination of the shear modulus is more preferably set at 95° C. thanat 80° C., from the viewpoints of reproducibility and precision in thedetermination. The thickness of the heat-expandable pressure-sensitiveadhesive layer is more preferably set at about 2.0 mm than at about 1.0mm, from the viewpoint of reducing the error in thickness of theheat-expandable pressure-sensitive adhesive layer.

The shear modulus of the pressure-sensitive adhesive constituting theheat-expandable pressure-sensitive adhesive layer can be controlled byadjusting the types and contents of base polymers and additives, such ascrosslinking agents and tackifiers, in the pressure-sensitive adhesive,and the type and content of the foaming agent such as heat-expandablemicrospheres.

The heat-expandable pressure-sensitive adhesive layer comprises apressure-sensitive adhesive for imparting tackiness, and a foaming agentfor imparting thermal expandability, as is described above.Consequently, the heat-peelable pressure-sensitive adhesive sheet can beeasily peeled off from an adherend by heating at any arbitrary timeafter the heat-peelable pressure-sensitive adhesive sheet is, forexample, applied to the adherend including a member or component such asa semiconductor wafer by using the pressure-sensitive adhesive layer[the pressure-sensitive adhesive layer having a shear modulus (23° C.)of less than 7×10⁶ Pa] arranged on or above the heat-expandablepressure-sensitive adhesive layer. In this procedure, theheat-expandable pressure-sensitive adhesive layer is heated to therebyallow the foaming agent, such as heat-expandable microspheres, to foamand/or expand. Accordingly, the heat-expandable pressure-sensitiveadhesive layer expands, and this expansion reduces the adhesion area(contact area) between the adherend and the pressure-sensitive adhesivelayer arranged on or above the heat-expandable pressure-sensitiveadhesive layer to thereby reduce the adhesive strength of thepressure-sensitive adhesive layer.

The forming agent for use in the heat-expandable pressure-sensitiveadhesive layer can be preferably, but is not specifically limited to,heat-expandable microspheres. Each of these foaming agents can be usedalone or in combination. The heat-expandable microspheres(microcapsules) can be appropriately selected from among knownheat-expandable microspheres. The heat-expandable microspheres arepreferably those comprising a foaming agent formulated intomicrocapsules, because some foaming agents not formulated intomicrocapsules may not stably exhibit satisfactory peelability. Examplesof the heat-expandable microspheres for use herein are microspherescomprising elastic shells and a substance contained therein, whichsubstance can easily gasify and expand by heating, such as isobutane,propane, or pentane. The shells often comprise a thermofusible materialor a material that breaks as a result of thermal expansion. Materialsfor constituting the shells include vinylidene chloride-acrylonitrilecopolymers, poly(vinyl alcohol)s, poly(vinyl butyral)s, poly(methylmethacrylate)s, polyacrylonitriles, poly(vinylidene chloride)s, andpolysulfones. The heat-expandable microspheres can be prepared accordingto a conventional procedure such as coacervation or interfacialpolymerization. The heat-expandable microspheres can also be obtained ascommercial products such as the products of Matsumoto Yushi-Seiyaku Co.,Ltd. under the trade name of “Matsumoto Microsphere”.

The foaming agent for use in the present invention can also be any otherfoaming agents than heat-expandable microspheres. Any foaming agentssuch as inorganic foaming agents and organic foaming agents can beappropriately selected as the foaming agent. Representative examples ofinorganic foaming agents include ammonium carbonate, ammonium hydrogencarbonate, sodium hydrogen carbonate, ammonium nitrite, sodiumborohydroxide, and azides. Representative examples of organic foamingagents include water; chlorofluoroalkane compounds such astrichloromonofluoromethane and dichloromonofluoromethane; azo compoundssuch as azobisisobutyronitrile, azodicarbonamide, and bariumazodicarboxylate; hydrazine compounds such as p-toluenesulfonylhydrazide, diphenylsulfone-3,3′-disulfonyl hydrazide,4,4′-oxybis(benzenesulfonyl hydrazide), and allylbis(sulfonylhydrazide); semicarbazide compounds such as p-toluoylenesulfonylsemicarbazide, and 4,4′-oxybis(benzenesulfonyl semicarbazide); triazolecompounds such as 5-morpholyl-1,2,3,4-thiatriazole; and N-nitrosocompounds such as N,N′-dinitrosopentamethylenetetramine andN,N′-dimethyl-N,N′-dinitrosoterephthalamide.

The thermal expansion starting temperature (foam initiating temperature)of the foaming agent such as heat-expandable microspheres is notspecifically limited but is preferably higher than 80° C. and morepreferably higher than 95° C. The thermal expansion starting temperatureof the foaming agent such as heat-expandable microspheres is, forexample, preferably about 85° C. to about 200° C., more preferably about100° C. to about 200° C., and particularly preferably about 100° C. toabout 170° C.

The “thermal expansion starting temperature (foam initiatingtemperature)” of the foaming agent such as heat-expandable microspheresin the present invention means the temperature at which the foamingagent begins expanding (foaming) upon heating. It corresponds typicallyto the peel initiating temperature of the heat-peelablepressure-sensitive adhesive sheet including the heat-expandablepressure-sensitive adhesive layer containing the foaming agent such asheat-expandable microspheres. The peel initiating temperature of theheat-peelable pressure-sensitive adhesive sheet can be, for example, theminimum (lowest) heat treatment temperature at which the adhesivestrength of the heat-expandable pressure-sensitive adhesive layercontaining the foaming agent such as heat-expandable microspheres can bereduced, as a result of heat treatment, to 10% or less of the adhesivestrength before heating. Accordingly, the thermal expansion startingtemperature of the foaming agent such as heat-expandable microspherescan be determined by measuring the peel initiating temperature of theheat-peelable pressure-sensitive adhesive sheet including theheat-expandable pressure-sensitive adhesive layer containing the foamingagent such as heat-expandable microspheres. Namely, it can be determinedby measuring the minimum (lowest) heat treatment temperature at whichthe adhesive strength of the heat-expandable pressure-sensitive adhesivelayer containing the foaming agent such as heat-expandable microspherescan be reduced, as a result of heat treatment, to 10% or less of theadhesive strength before heating. More specifically, the thermalexpansion starting temperature can be determined in the followingmanner. A poly(ethylene terephthalate) film [the product of TorayIndustries, Ltd. under the trade name of “Lumirror S10 #25”; hereinafteralso referred to as “PET film”] having a width of 20 mm and a thicknessof 23 μm is applied to the surface of the heat-expandablepressure-sensitive adhesive layer of a sample heat-peelablepressure-sensitive adhesive sheet, containing the foaming agent such asheat-expandable microspheres, using a hand roller so as not includebubbles to thereby yield a test piece. Thirty minutes into theapplication, the PET film is peeled off from the adhesive sheet at apeel angle of 180 degrees, and the adhesive strength herein is measuredat a measurement temperature of 23° C., a rate of pulling of 300 mm/min,and a peel angle of 180 degrees. The measured adhesive strength isdefined as the “initial adhesive strength”. Another test piece preparedby the above procedure is placed in a circotherm drier set at eachtemperature (heat treatment temperature) for one minute, is then takenout from the circotherm drier, and is left stand at 23° C. for twohours. Next, the PET film is peeled off from the adhesive sheet at apeel angle of 180 degrees, and the adhesive strength herein is measuredat a measurement temperature of 23° C., a rate of pulling of 300 mm/min,and a peel angle of 180 degrees. The measured adhesive strength isdefined as the “adhesive strength after heat treatment”. Next, theminimum (lowest) heat treatment temperature at which the adhesivestrength after heat treatment is 10% or less of the initial adhesivestrength is determined. The minimum (lowest) heat treatment temperaturecan be used as the thermal expansion starting temperature of the foamingagent such as heat-expandable microspheres.

The foaming agent preferably has such a suitable strength as not toburst or blow even at a coefficient of cubic expansion of 5 times ormore, more preferably 7 times or more, particularly preferably 10 timesor more. By satisfying this, the adhesive strength of theheat-expandable pressure-sensitive adhesive layer may be efficiently andstably reduced by heat treatment.

The amount of the foaming agent such as heat-expandable microspheres canbe suitably set according to the coefficient of expansion and the degreeof reduction in adhesive strength of the heat-expandablepressure-sensitive adhesive layer, and is generally, for example, 1 to150 parts by weight, preferably 10 to 130 parts by weight, and morepreferably 25 to 100 parts by weight, to 100 parts by weight of the basepolymer of the pressure-sensitive adhesive constituting theheat-expandable pressure-sensitive adhesive layer.

The particle size (average particle diameter) of heat-expandablemicrospheres, if used as the foaming agent, can be appropriately setaccording typically to the thickness of the heat-expandablepressure-sensitive adhesive layer. The average particle diameter of theheat-expandable microspheres can be selected within the range of, forexample, 100 μm or less, preferably 80 μm or less, more preferably 1 to50 μm, and particularly preferably 1 to 30 μm. The control of theparticle size of the heat-expandable microspheres can be carried outduring the preparation of the heat-expandable microspheres, or typicallyby classification after the preparation.

The pressure-sensitive adhesive used for constituting theheat-expandable pressure-sensitive adhesive layer can be apressure-sensitive adhesive having a shear modulus (23° C.) after beingcured or dried of 7×10⁶ Pa or more, and preferably 1×10⁷ Pa or more.Among such pressure-sensitive adhesives, preferred are those having ashear modulus (23° C.) after being cured or dried of 7×10⁶ Pa or more,preferably 1×10⁷ Pa or more, and having a shear modulus (80° C.) afterbeing cured or dried of less than 7×10⁶ Pa, preferably 5×10⁶ Pa or less,of which more preferred are those having a shear modulus (23° C.) afterbeing cured or dried of 7×10⁶ Pa or more, preferably 1×10⁷ Pa or more,and having a shear modulus (95° C.) after being cured or dried of lessthan 7×10⁶ Pa, preferably 5×10⁶ Pa or less.

The pressure-sensitive adhesive is not specifically limited, as long asit has the above-mentioned properties, but is preferably one that showsminimum restriction on the foaming and/or expansion of the foaming agentsuch as heat-expandable microspheres upon heating. Thepressure-sensitive adhesive can be selected as a pressure-sensitiveadhesive having the above-mentioned properties, from among knownpressure-sensitive adhesives. Examples thereof include rubberpressure-sensitive adhesives, acrylic pressure-sensitive adhesives,vinyl alkyl ether pressure-sensitive adhesives, siliconepressure-sensitive adhesives, polyester pressure-sensitive adhesives,polyamide pressure-sensitive adhesives, urethane pressure-sensitiveadhesives, fluorine-containing pressure-sensitive adhesives,styrene-diene block copolymer pressure-sensitive adhesives, andpressure-sensitive adhesives being modified in creep behavior byincorporating a hot melt resin having a melting point of about 200° C.or below to these pressure-sensitive adhesives. Such pressure-sensitiveadhesives can be found in, for example, JP-A No. Sho 56-61468, JP-A No.Sho 61-174857, JP-A No. Sho 63-17981, and JP-A No. Sho 56-13040.Radiation-curable pressure-sensitive adhesives or energy ray-curablepressure-sensitive adhesives can also be used as the pressure-sensitiveadhesive. Each of these pressure-sensitive adhesives can be used aloneor in combination.

When two or more different pressure-sensitive adhesives constitute thepressure-sensitive adhesive herein, the resulting pressure-sensitiveadhesive must essentially have the above-mentioned properties.

Rubber pressure-sensitive adhesives and acrylic pressure-sensitiveadhesives are preferred as the pressure-sensitive adhesive, of whichacrylic pressure-sensitive adhesives are more preferred. Examples ofrubber pressure-sensitive adhesives are rubber pressure-sensitiveadhesives comprising various natural rubbers and synthetic rubbers asbase polymers. Such rubbers include polyisoprene rubber,styrene-butadiene (SB) rubber, styrene-isoprene (SI) rubber,styrene-isoprene-styrene block copolymer (SIS) rubber,styrene-butadiene-styrene block copolymer (SBS) rubber,styrene-ethylene-butylene-styrene block copolymer (SEBS) rubber,styrene-ethylene-propylene-styrene block copolymer (SEPS) rubber,styrene-ethylene-propylene block copolymer (SEP) rubber, reclaimedrubber, butyl rubber, polyisobutylenes, and modified products of these.

The acrylic pressure-sensitive adhesives include acrylicpressure-sensitive adhesives comprising acrylic polymers (homopolymersor copolymers) as base polymers, the acrylic polymers each use one ormore (meth)acrylic acid alkyl esters as monomer components. Examples of(meth)acrylic acid alkyl esters for use in the acrylicpressure-sensitive adhesives include (meth)acrylic acid C₁₋₂₀ alkylesters such as methyl (meth)acrylates, ethyl (meth)acrylates, propyl(meth)acrylates, isopropyl (meth)acrylates, butyl (meth)acrylates,isobutyl (meth)acrylates, s-butyl (meth)acrylates, t-butyl(meth)acrylates, pentyl (meth)acrylates, hexyl (meth)acrylates, heptyl(meth)acrylates, octyl (meth)acrylates, 2-ethylhexyl (meth)acrylates,isooctyl (meth)acrylates, nonyl (meth)acrylates, isononyl(meth)acrylates, decyl (meth)acrylates, isodecyl (meth)acrylates,undecyl (meth)acrylates, dodecyl (meth)acrylates, tridecyl(meth)acrylates, tetradecyl (meth)acrylates, pentadecyl (meth)acrylates,hexadecyl (meth)acrylates, heptadecyl (meth)acrylates, octadecyl(meth)acrylates, nonadecyl (meth)acrylates, and eicosyl (meth)acrylates,of which (meth)acrylic acid C₄₋₁₈ alkyl (straight- or branched-chainalkyl) esters are preferred.

The acrylic polymers may further comprise one or more unitscorresponding to other monomer components that are copolymerizable withthe (meth)acrylic acid alkyl esters, for the purpose of improving, forexample, the cohesive force, thermal stability, and/or crosslinkingproperty. Such monomer components include, for example,carboxyl-containing monomers such as acrylic acid, methacrylic acid,carboxyethyl acrylate, carboxypentyl acrylate, itaconic acid, maleicacid, fumaric acid, and crotonic acid; acid anhydride group-containingmonomers such as maleic anhydride and itaconic anhydride;hydroxyl-containing monomers such as hydroxyethyl (meth)acrylates,hydroxypropyl (meth)acrylates, hydroxybutyl (meth)acrylates,hydroxyhexyl (meth)acrylates, hydroxyoctyl (meth)acrylates, hydroxydecyl(meth)acrylates, hydroxylauryl (meth)acrylates, and(4-hydroxymethylcyclohexyl)methyl methacrylate; sulfonicgroup-containing monomers such as styrenesulfonic acid, allylsulfonicacid, 2-(meth)acrylamido-2-methylpropanesulfonic acid,(meth)acrylamidopropanesulfonic acid, sulfopropyl (meth)acrylates, and(meth)acryloyloxynaphthalenesulfonic acid; phosphoric group-containingmonomers such as 2-hydroxyethylacryloyl phosphate; (N-substituted) amidemonomers such as (meth)acrylamides, N,N-dimethyl(meth)acrylamides,N-butyl(meth)acrylamides, N-methylol(meth)acrylamides, andN-methylolpropane(meth)acrylamides; aminoalkyl (meth)acrylate monomerssuch as aminoethyl (meth)acrylates, N,N-dimethylaminoethyl(meth)acrylates, and t-butylaminoethyl (meth)acrylates; alkoxyalkyl(meth)acrylate monomers such as methoxyethyl (meth)acrylates andethoxyethyl (meth)acrylates; maleimide monomers such asN-cyclohexylmaleimide, N-isopropylmaleimide, N-laurylmaleimide, andN-phenylmaleimide; itaconimide monomers such as N-methylitaconimide,N-ethylitaconimide, N-butylitaconimide, N-octylitaconimide,N-2-ethylhexylitaconimide, N-cyclohexylitaconimide, andN-laurylitaconimide; succinimide monomers such asN-(meth)acryloyloxymethylenesuccinimide,N-(meth)acryloyl-6-oxyhexamethylenesuccinimide, andN-(meth)acryloyl-8-oxyoctamethylenesuccinimide; vinyl monomers such asvinyl acetate, vinyl propionate, N-vinylpyrrolidone,methylvinylpyrrolidone, vinylpyridine, vinylpiperidone, vinylpyrimidine,vinylpiperazine, vinylpyrazine, vinylpyrrole, vinylimidazole,vinyloxazole, vinylmorpholine, N-vinylcarboxamides, styrene,α-methylstyrene, and N-vinylcaprolactam; cyano acrylate monomers such asacrylonitrile and methacrylonitrile; epoxy group-containing acrylicmonomers such as glycidyl (meth)acrylates; glycol acrylate monomers suchas polyethylene glycol (meth)acrylates, polypropylene glycol(meth)acrylates, methoxyethylene glycol (meth)acrylates, andmethoxypolypropylene glycol (meth)acrylates; acrylate monomerscontaining, for example, a heterocyclic ring, halogen atom, or siliconatom, such as tetrahydrofurfuryl (meth)acrylates, fluorine(meth)acrylates, and silicone (meth)acrylates; polyfunctional monomerssuch as hexanediol di(meth)acrylates, (poly)ethylene glycoldi(meth)acrylates, (poly)propylene glycol di(meth)acrylates, neopentylglycol di(meth)acrylates, pentaerythritol di(meth)acrylates,trimethylolpropane tri(meth)acrylates, pentaerythritoltri(meth)acrylates, dipentaerythritol hexa(meth)acrylates, epoxyacrylates, polyester acrylates, urethane acrylates, divinylbenzene,butyl di(meth)acrylates, and hexyl di(meth)acrylates; olefinic monomerssuch as isoprene, butadiene, and isobutylene; and vinyl ether monomerssuch as vinyl ether. Each of these monomer components can be used aloneor in combination.

The pressure-sensitive adhesive may further comprise suitable additivesaccording typically to the type of the pressure-sensitive adhesive, inaddition to polymer components such as a pressure-sensitive adhesivecomponent (base polymer). Such additives include, for example,crosslinking agents such as polyisocyanates and alkyl etherifiedmelamine compounds; tackifiers including those which are solid,semi-solid, or liquid at ordinary temperature, typically comprisingrosin derivative resins, polyterpene resins, petroleum resins, andoil-soluble phenolic resins; plasticizers; fillers; and age resistors(antioxidants).

The heat-expandable pressure-sensitive adhesive layer can be formedaccording to a conventional procedure. For example, it can be formed bymixing the pressure-sensitive adhesive and the foaming agent such asheat-expandable microspheres, where necessary with a solvent and otheradditives, and forming the mixture into a sheet-like layer. Morespecifically, the heat-expandable pressure-sensitive adhesive layer canbe formed, for example, by a process of applying the mixture to thesubstrate or the after-mentioned organic rubber-like elastic layer,which mixture contains the pressure-sensitive adhesive, the foamingagent such as heat-expandable microspheres, where necessary with asolvent and other additives; or by a process of applying the mixture toa suitable separator such as release paper to form a heat-expandablepressure-sensitive adhesive layer, and transferring the layer onto thesubstrate or the organic rubber-like elastic layer. The application ofthe heat-expandable pressure-sensitive adhesive layer can use a devicethat is generally used in spin coating or in a regularpressure-sensitive adhesive applicator, such as fan tender coater orkiss coater.

The heat-expandable pressure-sensitive adhesive layer may comprise asingle layer or multiple layers.

The thickness of the heat-expandable pressure-sensitive adhesive layercan be appropriately selected according typically to the degree ofreduction in adhesive strength and is generally about 5 to about 300 μm,and preferably about 20 to about 150 μm. When heat-expandablemicrospheres are used as the foaming agent, the thickness of theheat-expandable pressure-sensitive adhesive layer is preferably greaterthan the largest particle size of the heat-expandable microspherescontained therein. A heat-expandable pressure-sensitive adhesive layerhaving an excessively small thickness may have poor surface smoothnessdue to protrusions and depressions caused by the heat-expandablemicrospheres and have decreased adhesiveness before heating (in anunfoamed state). This heat-expandable pressure-sensitive adhesive layermay also show less deformation upon heat treatment to thereby have anadhesive strength not smoothly decreasing. In contrast, aheat-expandable pressure-sensitive adhesive layer having an excessivelylarge thickness may often undergo cohesive failure after foaming as aresult of heat treatment.

(Pressure-Sensitive Adhesive Layer)

The pressure-sensitive adhesive layer arranged on or above theheat-expandable pressure-sensitive adhesive layer (hereinafter alsoreferred to as “surface pressure-sensitive adhesive layer”) is used as apressure-sensitive adhesive layer to be applied or to adhere to anadherend. The surface pressure-sensitive adhesive layer has a feature ofhaving a shear modulus (23° C.) of less than 7×10⁶ Pa, as is describedabove. The shear modulus (23° C.) is preferably 5×10⁶ Pa or less, Thesurface pressure-sensitive adhesive layer can thereby exhibit excellentadhesiveness at ordinary temperature (23° C.). Accordingly, theheat-peelable pressure-sensitive adhesive sheet can be easily applied tothe adherend even at ordinary temperature, because the surfacepressure-sensitive adhesive layer can exhibit excellent adhesiveness atordinary temperature.

A pressure-sensitive adhesive constituting the surfacepressure-sensitive adhesive layer can be a pressure-sensitive adhesivewhich will have a shear modulus (23° C.) of less than 7×10⁶ Pa,preferably 5×10⁶ Pa or less, after being cured or dried. Thepressure-sensitive adhesive constituting the surface pressure-sensitiveadhesive layer is not specifically limited, as long as it has theabove-mentioned properties. It can be any of known or conventionalpressure-sensitive adhesives including those exemplified aspressure-sensitive adhesives for use in the heat-expandablepressure-sensitive adhesive layer. Examples of such pressure-sensitiveadhesives include rubber pressure-sensitive adhesives, acrylicpressure-sensitive adhesives, vinyl alkyl ether pressure-sensitiveadhesives, silicone pressure-sensitive adhesives, polyesterpressure-sensitive adhesives, polyamide pressure-sensitive adhesives,urethane pressure-sensitive adhesives, fluorine-containingpressure-sensitive adhesives, styrene-diene block copolymerpressure-sensitive adhesives, pressure-sensitive adhesives modified increep behaviour, and radiation-curable pressure-sensitive adhesives.Each of these pressure-sensitive adhesives can be used alone or incombination. The pressure-sensitive adhesive for constituting thesurface pressure-sensitive adhesive layer may further comprise known orconventional additives such as plasticizers, fillers, surfactants, ageresistors (antioxidants), and tackifiers.

The surface pressure-sensitive adhesive layer may expand upon heating,but preferably does not expand upon heating. Specifically, the surfacepressure-sensitive adhesive layer is preferably a non-heat-expandablepressure-sensitive adhesive layer.

The thickness of the surface pressure-sensitive adhesive layer is notspecifically limited, but can be set within the range of 0.01 to 10 μm,preferably 0.02 to 5 μm, and more preferably about 0.05 to 2 μm. Asurface pressure-sensitive adhesive layer having an excessively largethickness may absorb the peel force as a result of foaming of theheat-expandable pressure-sensitive adhesive layer by heating, and thismay invite reduced heat-peelability of the adhesive sheet. In contrast,a surface pressure-sensitive adhesive layer having an excessively smallthickness may not sufficiently develop its tackiness and fail to firmlyfix the adherend.

The surface pressure-sensitive adhesive layer can be formed by the sameprocedure as in the heat-expandable pressure-sensitive adhesive layer.For example, it can be formed by coating a material mixture to thesubstrate; or by applying the mixture to a separator and thentransferring the resulting layer onto the substrate. The application ofthe surface pressure-sensitive adhesive layer can use a device that isgenerally used in spin coating or in a regular pressure-sensitiveadhesive applicator, such as fan tender coater or kiss coater.

The surface pressure-sensitive adhesive layer can comprise a singlelayer or multiple layers.

(Intermediate Layer)

The heat-peelable pressure-sensitive adhesive sheets according to thepresent invention may further comprise one or more intermediate layers.Such intermediate layers include a coating layer of a release agent forimparting peelability, and a primer coating layer for improving theadhesion strength. Other intermediate layers than the release agentcoating layer and the primer coating layer include, for example, a layerfor imparting satisfactory deformability; a layer for increasing theadhesion area with an adherend such as a semiconductor wafer; a layerfor improving the adhesive strength; a layer for enabling the sheet tolie in good accordance with the surface of the adherend such as asemiconductor wafer; a layer for improving the treating ability inreduction of the adhesive strength by heating; and a layer for improvingthe peelability of the sheet from the adherend such as a semiconductorwafer after heating. Among them, an organic rubber-like elastic layer ispreferably arranged as an intermediate layer between the substrate andthe heat-expandable pressure-sensitive adhesive layer as illustrated inFIG. 1, from the viewpoints typically of imparting deformability to theheat-peelable pressure-sensitive adhesive sheet.

The heat-peelable pressure-sensitive adhesive sheet 1 illustrated inFIG. 1 comprises a heat-expandable pressure-sensitive adhesive layer 4arranged above a substrate 2 with the interposition of an organicrubber-like elastic layer 3. By arranging the organic rubber-likeelastic layer, the heat-peelable pressure-sensitive adhesive sheet, whenapplied to an adherend, enables its surface (the surface of theheat-expandable pressure-sensitive adhesive layer) to lie in goodaccordance with the surface of the adherend to thereby have an increasedadhesion area. The heat-peelable pressure-sensitive adhesive sheet cancontrol the expansion of the heat-expandable pressure-sensitive adhesivelayer with good precision upon heating to thereby allow theheat-expandable pressure-sensitive adhesive layer to expandpreferentially in a thickness direction uniformly, when the sheet ispeeled off from the adherend by heating. Specifically, the organicrubber-like elastic layer can act to provide a larger adhesion area uponthe adhesion of the heat-peelable pressure-sensitive adhesive sheet withthe adherend, because the surface of the adhesive sheet can lie insatisfactory accordance with the surface dimensions of the adhered. Inaddition, it can act to reduce the constraint of the foaming and/orexpansion of the heat-peelable pressure-sensitive adhesive sheet in aplane direction when the heat-expandable pressure-sensitive adhesivelayer is heated to allow the layer to foam and/or expand so as to peeloff the heat-peelable pressure-sensitive adhesive sheet from theadherend. In other words, it can act to promote the formation ofwaviness structure due to three-dimensional structural change of theheat-expandable pressure-sensitive adhesive layer.

The organic rubber-like elastic layer is a layer that is providedaccording to necessary, and is not always necessary.

The organic rubber-like elastic layer is preferably arranged upon theheat-expandable pressure-sensitive adhesive layer on its side facing thesubstrate so as to superimpose the heat-expandable pressure-sensitivelayer. The organic rubber-like elastic layer can also be arranged as alayer other than the intermediate layer between the substrate and theheat-expandable pressure-sensitive adhesive layer. The organicrubber-like elastic layer can be arranged on or above one or both sidesof the substrate.

The organic rubber-like elastic layer preferably comprises a naturalrubber, a synthetic rubber, or a synthetic resin showing rubberelasticity, each of which has a Shore D hardness according to ASTMD-2240 of, for example, 50 or less, and particularly preferably 40 orless. The synthetic rubbers or synthetic resins showing rubberelasticity include, for example, synthetic rubbers such as nitrilerubbers, diene rubbers, and acrylic rubbers; thermoplastic elastomerssuch as polyolefin elastomers and polyester elastomers; and syntheticresins showing rubber elasticity, such as ethylene-vinyl acetatecopolymers, polyurethanes, polybutadienes, and flexible poly(vinylchloride)s. In this connection, inherently rigid polymers such aspoly(vinyl chloride)s can exhibit rubber elasticity by incorporatingcompounding ingredients such as plasticizers or flexibilizers into them.The resulting compositions can also be used as materials forconstituting the organic rubber-like elastic layer. Pressure-sensitiveadhesive substances, such as pressure-sensitive adhesives constitutingthe heat-expandable pressure-sensitive adhesive layer, can also be usedas materials for constituting the organic rubber-like elastic layer.

The organic rubber-like elastic layer can be formed, for example, byapplying a coating composition to the substrate, which coatingcomposition comprises materials for constituting the organic rubber-likeelastic layer, such as the natural rubber, synthetic rubber, orsynthetic resin showing rubber elasticity (coating); by bonding thesubstrate with a film formed from the material for forming the organicrubber-like elastic layer or with a multilayer film comprising one ormore heat-expandable pressure-sensitive adhesive layers, and a layercomprising the material for the organic rubber-like elastic layerarranged thereon (dry lamination); or by coextruding a resin substrate,with a resin composition comprising the material for the organicrubber-like elastic layer (co-extrusion).

The organic rubber-like elastic layer may comprise a pressure-sensitiveadhesive substance mainly containing a natural rubber, a syntheticrubber, or a synthetic resin showing rubber elasticity or may be formedfrom a foamed film mainly containing the component. The foaming hereincan be carried out according to a conventional procedure, such asmechanical stirring; using a gas produced as a result of reaction; usinga foaming agent; removing soluble matters; spraying; forming a syntacticfoam; or sintering.

The thickness of an intermediate layer such as the organic rubber-likeelastic layer is, for example, about 5 to about 300 μm, and preferablyabout 20 to about 150 μm. An intermediate layer such as an organicrubber-like elastic layer having an excessively small thickness may notinduce the three-dimensional structural change after heating and foamingto thereby impair the peelability. The intermediate layer such as anorganic rubber-like elastic layer may comprise a single layer ormultiple layers.

When a radiation curable substance is used typically in theheat-expandable pressure-sensitive adhesive layer, the intermediatelayer such as an organic rubber-like elastic layer is preferably onethat does not inhibit the transmission of the radiation.

(Separator)

The adhesive sheet in FIG. 1 comprises a separator (release liner) as aprotecting member for the pressure-sensitive adhesive layer (surfacepressure-sensitive adhesive layer) arranged on or above theheat-expandable pressure-sensitive adhesive layer. However, theseparator is not always necessary. Such a separator (release liner) canbe arranged as a protecting member for another pressure-sensitiveadhesive layer, if arranged, than the surface pressure-sensitiveadhesive layer.

The separator is peeled off when the pressure-sensitive adhesive layerprotected by the separator is in use. In other words, the separator ispeeled off when the pressure-sensitive adhesive layer protected by theseparator is applied to the adherend.

The separator can be, for example, a conventional release paper.Specific examples of the separator include bases having a release layerof a plastic film or paper which surface is treated with a release agentsuch as a silicone, long-chain alkyl, fluorine, or molybdenum sulfiderelease agent; low-adhesive bases comprising fluorine-containingpolymers such as polytetrafluoroethylenes, polychlorotrifluoroethylenes,poly(vinyl fluoride)s, poly(vinylidene fluoride)s,tetrafluoroethylene-hexafluoropropylene copolymers, andchlorofluoroethylene-vinylidene fluoride copolymers; and low-adhesivebases comprising non-polar polymers including olefinic resins such aspolyethylenes and polypropylenes. The separator can also be used as asubstrate for supporting the heat-expandable pressure-sensitive adhesivelayer.

The separator can be formed according to a known or conventionalprocedure. The thickness and other parameters of the separator are notspecifically limited.

(Other Layers)

The heat-peelable pressure-sensitive adhesive sheets have only tocomprise a heat-expandable pressure-sensitive adhesive layer and asurface pressure-sensitive adhesive layer arranged in this order on orabove at least one side of a substrate. They include, for example, (1) aheat-peelable pressure-sensitive adhesive sheet comprising a substrate,and a heat-expandable pressure-sensitive adhesive layer and apressure-sensitive adhesive layer arranged in this order on or above oneside of the substrate; (2) a heat-peelable pressure-sensitive adhesivesheet comprising a substrate, and a heat-expandable pressure-sensitiveadhesive layer and a pressure-sensitive adhesive layer arranged in thisorder on or above both sides of the substrate; and (3) a heat-peelablepressure-sensitive adhesive sheet comprising a substrate, and aheat-expandable pressure-sensitive adhesive layer and apressure-sensitive adhesive layer arranged in this order on or aboveboth sides of the substrate, and a non-heat-expandablepressure-sensitive adhesive layer (a pressure-sensitive adhesive layerhaving no expandability upon heating) arranged on or above the otherside of the substrate. When heat-expandable pressure-sensitive adhesivelayers are arranged on or above both sides of the substrate, it isenough that at least one of the heat-expandable pressure-sensitiveadhesive layers satisfies the above-mentioned requirements. Theseheat-peelable pressure-sensitive adhesive sheets may further comprise,for example, one or more intermediate layers, such as organicrubber-like elastic layers, arranged between the substrate and theheat-expandable pressure-sensitive adhesive layer.

(Non-Heat-Expandable Pressure-Sensitive Adhesive Layer)

The pressure-sensitive adhesive for constituting the non-heat-expandablepressure-sensitive adhesive layer is not specifically limited and can beany known or conventional pressure-sensitive adhesives including thoseexemplified as pressure-sensitive adhesives for use in theheat-expandable pressure-sensitive adhesive layer. Examples of suchpressure-sensitive adhesives are rubber pressure-sensitive adhesives,acrylic pressure-sensitive adhesives, vinyl alkyl etherpressure-sensitive adhesives, silicone pressure-sensitive adhesives,polyester pressure-sensitive adhesives, polyamide pressure-sensitiveadhesives, urethane pressure-sensitive adhesives, fluorine-containingpressure-sensitive adhesives, styrene-diene block copolymerpressure-sensitive adhesives, pressure-sensitive adhesives modified increep behavior, and radiation-curable pressure-sensitive adhesives. Eachof these pressure-sensitive adhesives can be used alone or incombination. The pressure-sensitive adhesive for constituting thenon-heat-expandable pressure-sensitive adhesive layer may furthercomprise known or conventional additives such as plasticizers, fillers,surfactants, age resistors (antioxidants), and tackifiers.

The thickness of the non-heat-expandable pressure-sensitive adhesivelayer can be 300 μm or less, for example, 1 to 300 μm, and preferably 5to 100 μm. The non-heat-expandable pressure-sensitive adhesive layer canbe formed by the same procedure as with the heat-expandablepressure-sensitive adhesive layer and the surface pressure-sensitiveadhesive layer, for example, by applying a material mixture to thesubstrate or by applying the mixture to a separator to form apressure-sensitive adhesive layer and transferring the formed layer tothe substrate. The non-heat-expandable pressure-sensitive adhesive layermay comprise a single layer or multiple layers.

The heat-peelable pressure-sensitive adhesive sheets according to thepresent invention may be double-sided adhesive sheets having twoadhesive surfaces but are preferably one-sided adhesive sheets having anadhesive surface on one side. Accordingly, the heat-peelablepressure-sensitive adhesive sheets are preferably those comprising asubstrate, and a heat-expandable pressure-sensitive adhesive layer and asurface pressure-sensitive adhesive layer arranged in this order on oneside of the substrate.

The heat-peelable pressure-sensitive adhesive sheet may be wound andformed into a roll or may constitute a multilayer sheet comprisingplural plies of sheets. The heat-peelable pressure-sensitive adhesivesheet, if wound into a roll, can be prepared typically in the followingmanner. The sheet can be wound into a roll in such a condition that thepressure-sensitive adhesive layer (surface pressure-sensitive adhesivelayer) arranged on or above the heat-expandable pressure-sensitiveadhesive layer is protected by a separator. Namely, the heat-peelablepressure-sensitive adhesive sheet to be wound as a roll can comprise asubstrate, a heat-expandable pressure-sensitive adhesive layer arrangedon or above one side of the substrate, a pressure-sensitive adhesivelayer arranged on or above the heat-expandable pressure-sensitiveadhesive layer, a separator arranged on or above the pressure-sensitiveadhesive layer, and, if necessary, an intermediate layer, such as anorganic rubber-like elastic layer, arranged between the substrate andthe heat-expandable pressure-sensitive adhesive layer.

Such a heat-peelable pressure-sensitive adhesive sheet wound as a rollmay comprise a substrate, a heat-expandable pressure-sensitive adhesivelayer, and a surface pressure-sensitive adhesive layer arranged on orabove one side of the substrate, and a strippable layer (back-treatedlayer) arranged on the other side of the substrate.

The heat-peelable pressure-sensitive adhesive sheets can be shaped into,for example, sheets or tapes.

The heat-peelable pressure-sensitive adhesive sheets according to thepresent invention have the above-mentioned configuration. Specifically,they comprise a heat-expandable pressure-sensitive adhesive layer havinga shear modulus (in an unfoamed state; 23° C.) of 7×10⁶ Pa or more, anda pressure-sensitive adhesive layer being arranged on or above theheat-expandable pressure-sensitive adhesive layer and having a shearmodulus (in an unfoamed state; 23° C.) of less than 7×10⁶ Pa.Accordingly, they can easily adhere to an adherend even at ordinarytemperature (23° C.) upon processing of the adherend. They can preventdeformation of the heat-expandable pressure-sensitive adhesive layer dueto pressurization in a pressing process upon processing of an adherendincluding the pressing process in the production of electroniccomponents. They can exhibit excellent tackiness and can be easilypeeled off from the processed article after processing typically in thelaminating and cutting processes in the production of electroniccomponents, and in the grinding and cutting processes in the productionof semiconductor components. Accordingly, they can exhibit suitableviscoelastic force and adhesive strength for fixing the adherend uponprocessing, and they can have reduced tackiness as a result of heatingand can therefore be easily peeled off or separated from the adherendwhen the adhesion should be released after achieving the targetadhesion. Thus, the heat-peelable pressure-sensitive adhesive sheetsaccording to the present invention can be advantageously used asheat-peelable pressure-sensitive adhesive sheets in processes forprocessing an adherend, including the pressing process in the productionof electronic components; the grinding and cutting processes in theproduction of semiconductor components; and the laminating and cuttingprocesses in the production of electronic components. The heat-peelablepressure-sensitive adhesive sheets can also be adherend upon conveying.

[Method of Processing an Adherend]

In the method of processing an adherend (work) according to the presentinvention, the adherend is processed by applying the adherend to thepressure-sensitive adhesive layer arranged on or above theheat-expandable pressure-sensitive adhesive layer of the heat-peelablepressure-sensitive adhesive sheet, and then subjecting the adherend toprocessing. The process in processing of the adherend can be arbitrarilyselected and may include a pressing process (pressing under pressure), alaminating process, and a cutting process in the production ofelectronic components, and a grinding process and a cutting process inthe production of semiconductor components. More specifically, processesupon processing of the adherend include the processes of printingelectrodes to a green sheet, such as a patterning process; laminatingprocess; pressing process (pressing under pressure); cutting processessuch as a lapping process and a dicing process; grinding processes suchas a back grinding process; firing process; and assembly process.

Upon such processing of an adherend, the pressing process in theproduction of electronic components requires the adhesive sheet to havea high shear modulus, and it is important to carry out the pressingprocess at room temperature (about 20° C. to about 25° C.) or attemperatures around room temperature (about 0° C. to about 60° C.).

In contrast, the laminating and cutting processes in the production ofelectronic components and the grinding and cutting processes in theproduction of semiconductor components, for example, require theadhesive sheet to have a high tackiness and to have a low shear modulus,and thereby the laminating and cutting processes, grinding and cuttingprocesses should be carried out after heating the adhesive sheet. Itshould be noted that the temperature in heating herein must be atemperature lower than the foam initiating temperature of the foamingagent in the heat-expandable pressure-sensitive adhesive layer. Theheating temperature herein is not specifically limited, as long as it isequal to or higher than room temperature and lower than the foaminitiating temperature of the foaming agent in the heat-expandablepressure-sensitive adhesive layer. It is preferably set within the rangeof, for example, about 50° C. to about 150° C., preferably about 80° C.to about 120° C., and more preferably about 90° C. to about 110° C.After once heating the adhesive sheet, the processing such aslaminating/cutting or grinding/cutting can be carried out whilemaintaining the work at the heating temperature or carried out aftercooling the work. Namely, the processing such as laminating/cutting orgrinding/cutting can be carried out at temperatures equal to or lowerthan the heating temperature. For example, it can be carried out attemperatures from room temperature to the heating temperature. Morespecifically, the processing such as laminating, cutting, grinding, andcutting can be carried out at room temperature after once cooling theheated article to room temperature, carried out while keeping thearticle at the heating temperature without cooling, or carried out attemperatures higher than room temperature after cooling the heatedarticle.

When the processing processes include the laminating and cuttingprocesses, or grinding and cutting processes, the heat-expandablepressure-sensitive adhesive layer preferably has a shear modulus (in anunfoamed state; 80° C.) of less than 7×10⁶ Pa, and particularlypreferably has a shear modulus (in an unfoamed state; 95° C.) of lessthan 7×10⁶ Pa.

As is described above, the conditions such as temperature can beappropriately adjusted according to the requirements in properties suchas elasticity and tackiness upon processing, in the method of processingan adherend according to the present invention.

After processing the adherend, particularly after achieving the targetadhesion or when the adhesion should be released, the processed adherendcan be peeled off or separated from the adhesive sheet to isolate theprocessed adherend (processed article) by heating to temperatures equalto or higher than the foam initiating temperature of the foaming agentin the heat-expandable pressure-sensitive adhesive layer and therebyreducing the tackiness of the pressure-sensitive adhesive layer arrangedon or above the heat-expandable pressure-sensitive adhesive layer.

The heat treatment for peeling or separating the processed adherend(processed article) can be carried out using a suitable heating deviceor procedure, such as a hot plate, a hot air dryer, a near-infraredlamp, or an air dryer. The heating temperature has only to be atemperature equal to or higher than the thermal expansion startingtemperature (foam initiating temperature) of the foaming agent, such asheat-expandable microspheres, in the heat-expandable pressure-sensitiveadhesive layer. The conditions of the heat treatment can beappropriately set according typically to the surface condition of theadherend, the degree of reduction in adhesion area due typically to thetype of the foaming agent such as heat-expandable microspheres, thethermal stabilities of the substrate and adherend, and heating proceduresuch as thermal capacity and heating device. The heat treatment can begenerally carried out at temperatures of 100° C. to 250° C. for 1 to 90seconds typically using a hot plate, or for 5 to 15 minutes typicallyusing a hot air dryer. The heat treatment can be carried out in anappropriate stage according to the purpose of use. The heat source mayalso be an infrared lamp or heated water.

[Adherend]

The article (adherend; work) to be held by the heat-peelablepressure-sensitive adhesive sheet can be freely selected. Specifically,examples of the adherend are various articles including articles to beelectronic components, such as silicon wafers and other semiconductorwafers, and semiconductor chips; articles to be semiconductorcomponents, such as silicon wafers; electric articles such as ceramiccapacitors and resonators; display devices such as liquid crystal cells;as well as thermal heads, solar cells, printed boards such as multilayerceramic sheets, and “green sheets”. Each of such adherends can be usedalone or in combination.

[Processed Adherend; Processed Article]

Various processed articles (processed adherends) can be obtainedaccording to the present invention, by applying the heat-peelablepressure-sensitive adhesive sheet to an For example, an article to be anelectronic component, such as a semiconductor wafer, as an adherend(work) can yield, for example, an electronic component or a circuitboard as a processed article. Likewise, an article to be a semiconductorcomponent, such as a silicon wafer, as an adhered can yield asemiconductor component such as a semiconductor chip as a processedarticle. Specifically, electronic components and semiconductorcomponents according to the present invention are produced by using themethod of processing an adherend and using the heat-peelablepressure-sensitive adhesive sheet.

EXAMPLES

The present invention will be illustrated in further detail withreference to several Examples below, which by no means limit the scopeof the present invention.

Example 1

A resin composition (mixture) was applied to a thickness after drying of25 μm to a polyester film 100 μm thick as a substrate, was dried, andthereby yielded an organic rubber-like elastic layer thereon. The resincomposition comprises 100 parts by weight of an acrylic copolymer (anacrylic copolymer comprising 100 parts by weight of butyl acrylate, 15parts by weight of acrylonitrile, and 5 parts by weight of acrylic acidas monomer components), 3 parts by weight of an isocyanate crosslinkingagent (the product of Nippon Polyurethane Industry Co., Ltd. under thetrade name of “Collonate L”), and toluene as a solvent.

Next, a heat-expandable pressure-sensitive adhesive layer was formed byapplying a film of a resin composition (mixture) to a thickness afterdrying of 40 μm to a separator, and drying the applied film. The resincomposition comprises 100 parts by weight of a maleic acid-modifiedstyrene-ethylene-butylene-styrene block copolymer [SEBS; having a weightratio of styrene block to ethylene-butylene block of 30/70, and an acidvalue of 10 (mg-CH₃ONa/g)], 3 parts by weight of an epoxy crosslinkingagent (the product of Mitsubishi Gas Chemical Company, Inc. under thetrade name of “TETRAD-C”), 50 parts by weight of heat-expandablemicrospheres (the product of Matsumoto Yushi-Seiyaku Co., Ltd. under thetrade name of “Matsumoto Microsphere F50D”; having a foam initiatingtemperature of 120° C. and an average particle diameter of 14 μm), andtoluene as a solvent.

The heat-expandable pressure-sensitive adhesive layer on the separatorwas adhered to the organic rubber-like elastic layer on the polyesterfilm so as to be in contact with each other, and thereby yielded apressure-sensitive adhesive sheet having a layer configuration of“substrate/(organic rubber-like elastic layer)/(heat-expandablepressure-sensitive adhesive layer)/separator”.

Next, after peeling off the separator, a pressure-sensitive adhesivelayer (surface pressure-sensitive adhesive layer) was formed on thepressure-sensitive adhesive sheet by applying a film of a resincomposition (mixture) to a thickness after drying of 0.5 μm to theheat-expandable pressure-sensitive adhesive layer using a gravurecoater, and drying the resulting film. The resin composition comprises100 parts by weight of an acrylic copolymer (an acrylic copolymercomprising 100 parts by weight of ethyl acrylate, 40 parts by weight of2-ethylhexyl acrylate, and 5 parts by weight of 2-hydroxyethyl acrylateas monomer components), 1.5 parts by weight of an isocyanatecrosslinking agent (the product of Nippon Polyurethane Industry Co.,Ltd. under the trade name of “Collonate L”), and toluene as a solvent.Thereafter, a separator was placed on the pressure-sensitive adhesivelayer, and thereby yielded a heat-peelable pressure-sensitive adhesivesheet having a layer configuration of “substrate/(organic rubber-likeelastic layer)/(heat-expandable pressure-sensitive adhesivelayer)/(pressure-sensitive adhesive layer)/separator”.

Example 2

A resin composition (mixture) was applied to a thickness after drying of15 μm to a polyester film as a substrate 50 μm thick, was dried, andthereby yielded an organic rubber-like elastic layer thereon. The resincomposition comprises 100 parts by weight of an acrylic copolymer (anacrylic copolymer comprising 50 parts by weight of 2-ethylhexylacrylate, 50 parts by weight of ethyl acrylate, and 5 parts by weight of2-hydroxyethyl acrylate as monomer components), 3 parts by weight of anisocyanate crosslinking agent (the product of Nippon PolyurethaneIndustry Co., Ltd. under the trade name of “Collonate L”), and tolueneas a solvent.

Next, a heat-expandable pressure-sensitive adhesive layer was formed byapplying a film of a resin composition (mixture) to a thickness afterdrying of 40 μm to a separator, and drying the resulting film. The resincomposition comprises 100 parts by weight of a maleic acid-modifiedstyrene-ethylene-butylene-styrene block copolymer [SEBS; having a weightratio of styrene block to ethylene-butylene block of 30/70, and an acidvalue of 10 (mg-CH₃ONa/g)], 1.5 parts by weight of an epoxy crosslinkingagent (the product of Mitsubishi Gas Chemical Company, Inc. under thetrade name of “TETRAD-C”), 40 parts by weight of heat-expandablemicrospheres (the product of Matsumoto Yushi-Seiyaku Co., Ltd. under thetrade name of “Matsumoto Microsphere F50D”; having a foam initiatingtemperature of 120° C. and an average particle diameter of 14 μm), 30parts by weight of a terpene phenolic resin (the product of YasuharaChemical Co., Ltd. under the trade name of “YS Polyster T130”), andtoluene as a solvent.

The heat-expandable pressure-sensitive adhesive layer on the separatorwas adhered to the organic rubber-like elastic layer on the polyesterfilm so as to be in contact with each other, and thereby yielded apressure-sensitive adhesive sheet having a layer configuration of“substrate/(organic rubber-like elastic layer)/(heat-expandablepressure-sensitive adhesive layer)/separator”.

Next, after peeling off the separator, a pressure-sensitive adhesivelayer (surface pressure-sensitive adhesive layer) was formed on thepressure-sensitive adhesive sheet by applying a film of a resincomposition (mixture) to a thickness after drying of 2 μm to theheat-expandable pressure-sensitive adhesive layer using a gravurecoater, and drying the resulting film. The resin composition comprises100 parts by weight of an acrylic copolymer (an acrylic copolymercomprising 50 parts by weight of 2-ethylhexyl acrylate, 50 parts byweight of ethyl acrylate, and 5 parts by weight of 2-hydroxyethylacrylate as monomer components), 3 parts by weight of an isocyanatecrosslinking agent (the product of Nippon Polyurethane Industry Co.,Ltd. under the trade name of “Collonate L”), and toluene as a solvent.Next, a separator was placed on the pressure-sensitive adhesive layerand thereby yielded a heat-peelable pressure-sensitive adhesive sheethaving a layer configuration of “substrate/(organic rubber-like elasticlayer)/(heat-expandable pressure-sensitive adhesivelayer)/(pressure-sensitive adhesive layer)/separator”.

Comparative Example 1

A resin composition (mixture) was applied to a thickness after drying of25 μm to a polyester film 100 μm thick as a substrate, was dried, andthereby yielded an organic rubber-like elastic layer thereon. The resincomposition comprises 100 parts by weight of an acrylic copolymer (anacrylic copolymer comprising 100 parts by weight of butyl acrylate, 15parts by weight of acrylonitrile, and 5 parts by weight of acrylic acidas monomer components), 3 parts by weight of an isocyanate crosslinkingagent (the product of Nippon Polyurethane Industry Co., Ltd. under thetrade name of “Collonate L”), and toluene as a solvent.

Next, a heat-expandable pressure-sensitive adhesive layer was formed byapplying a film of a resin composition (mixture) to a thickness afterdrying of 40 μm to a separator, and drying the applied film. The resincomposition comprises 100 parts by weight of a maleic acid-modifiedstyrene-ethylene-butylene-styrene block copolymer [SEBS; having a weightratio of styrene to ethylene-butylene block of 30/70, and an acid valueof 10 (mg-CH₃ONa/g)], 3 parts by weight of an epoxy crosslinking agent(the product of Mitsubishi Gas Chemical Company, Inc. under the tradename of “TETRAD-C”), 50 parts by weight of heat-expandable microspheres(the product of Matsumoto Yushi-Seiyaku Co., Ltd. under the trade nameof “Matsumoto Microsphere F50D”; having a foam initiating temperature of120° C. and an average particle diameter of 14 μm), and toluene as asolvent.

The heat-expandable pressure-sensitive adhesive layer on the separatorwas adhered to the organic rubber-like elastic layer on the polyesterfilm so as to be in contact with each other and thereby yielded aheat-peelable pressure-sensitive adhesive sheet having a layerconfiguration of “substrate/(organic rubber-like elasticlayer)/(heat-expandable pressure-sensitive adhesive layer)/separator”.

Namely, the heat-peelable pressure-sensitive adhesive sheet according toComparative Example 1 corresponds to the heat-peelablepressure-sensitive adhesive sheet according to Example 1, except for notforming the pressure-sensitive adhesive layer (surfacepressure-sensitive adhesive layer; having a thickness of 0.5 μm).

Comparative Example 2

A resin composition (mixture) was applied to a thickness after drying of15 μm to a polyester film as a substrate 50 μm thick, was dried, andthereby yielded an organic rubber-like elastic layer. The resincomposition comprises 100 parts by weight of an acrylic copolymer (anacrylic copolymer comprising 50 parts by weight of 2-ethylhexylacrylate, 50 parts by weight of ethyl acrylate, and 5 parts by weight of2-hydroxyethyl acrylate as monomer components), 3 parts by weight of anisocyanate crosslinking agent (the product of Nippon PolyurethaneIndustry Co., Ltd. under the trade name of “Collonate L”), and tolueneas a solvent.

Next, a heat-expandable pressure-sensitive adhesive layer was formed byapplying a film of a resin composition (mixture) to a thickness afterdrying of 40 μm to a separator, and drying the resulting film. The resincomposition comprises 100 parts by weight of a maleic acid-modifiedstyrene-ethylene-butylene-styrene block copolymer [SEBS; having a weightratio of styrene block to ethylene-butylene block of 30/70, and an acidvalue of 10 (mg-CH₃ONa/g)], 1.5 parts by weight of an epoxy crosslinkingagent (the product of Mitsubishi Gas Chemical Company, Inc. under thetrade name of “TETRAD-C”), 40 parts by weight of heat-expandablemicrospheres (the product of Matsumoto Yushi-Seiyaku Co., Ltd. under thetrade name of “Matsumoto Microsphere F50D”; having a foam initiatingtemperature of 120° C. and an average particle diameter of 14 μm), 30parts by weight of a terpene phenolic resin (the product of YasuharaChemical Co., Ltd. under the trade name of “YS Polyster T130”), andtoluene as a solvent.

The heat-expandable pressure-sensitive adhesive layer on the separatorwas adhered to the organic rubber-like elastic layer on the polyesterfilm so as to be in contact with each other, and thereby yielded apressure-sensitive adhesive sheet having a layer configuration of“substrate/(organic rubber-like elastic layer)/(heat-expandablepressure-sensitive adhesive layer)/separator”.

Namely, the heat-peelable pressure-sensitive adhesive sheet according toComparative Example 2 corresponds to the heat-peelablepressure-sensitive adhesive sheet according to Example 2, except for notforming the pressure-sensitive adhesive layer (surfacepressure-sensitive adhesive layer; having a thickness of 2 μm).

(Evaluations)

The heat-peelable pressure-sensitive adhesive sheets Examples 1 and 2were evaluated on shear modulus, tackiness, peelability upon heating,and misregistration of the heat-expandable pressure-sensitive adhesivelayer according to the following determination or evaluation methods.The results are shown in Table 1.

(Determination Method of Shear Modulus)

The shear modulus of the heat-expandable pressure-sensitive adhesivelayer on the separator was measured before it was adhered to the organicrubber-like elastic layer on the polyester film to yield theheat-peelable pressure-sensitive adhesive sheet. More specifically, theheat-expandable pressure-sensitive adhesive layer was peeled off fromthe separator, the peeled heat-expandable pressure-sensitive adhesivelayer was then set at a predetermined position of a dynamicviscoelasticity measuring instrument, the product of Rheometrics Inc.under the trade name of “ARES”, and the shear modulus of theheat-expandable pressure-sensitive adhesive layer in an unfoamed statewas determined under conditions of temperatures of 23° C., 80° C., and95° C., a frequency of 1 Hz, a sample thickness (the thickness of theheat-expandable pressure-sensitive adhesive layer) of about 2.0 mm, anda strain of 0.1% (23° C.) or 0.3% (80° C. and 95° C.), using a jigincluding parallel plates having a plate diameter of 7.9 mm. The sameresults as in the above case at a sample thickness of about 2 mm, wereobtained at a sample thickness of about 1 mm.

(Evaluation Method of Tackiness)

A sample heat-peelable pressure-sensitive adhesive sheet was cut to awidth of 20 mm, from which the separator was peeled off at ordinarytemperature (23° C.). Next, a poly(ethylene terephthalate) film (PETfilm; having a thickness of 25 μm) was applied to the surfacepressure-sensitive adhesive layer or heat-expandable pressure-sensitiveadhesive layer, and the 180° peel strength was measured immediatelyafter the application (without aging) by peeling the PET film at a rateof pulling of 300 mm/min and a temperature of 23° C. In this procedure,the PET film was adhered to the pressure-sensitive adhesive layer in thesamples according to Examples 1 and 2, and it was adhered to theheat-expandable pressure-sensitive adhesive layer in the samplesaccording to Comparative Examples 1 and 2.

(Evaluation Method of Peelability Upon Heating)

A sample heat-peelable pressure-sensitive adhesive sheet was cut to awidth of 20 mm, from which the separator was peeled off at ordinarytemperature (23° C.). Next, a poly(ethylene terephthalate) film (PETfilm; having a thickness of 25 μm) was applied to the surfacepressure-sensitive adhesive layer or heat-expandable pressure-sensitiveadhesive layer. In this procedure, the PET film was adhered to thepressure-sensitive adhesive layer in the samples according to Examples 1and 2, and it was adhered to the heat-expandable pressure-sensitiveadhesive layer in the samples according to Comparative Examples 1 and 2.Heating was then carried out at 130° C. for one minute, and how the PETfilm was peeled was visually observed.

(Evaluation Method of Misregistration of Heat-ExpandablePressure-Sensitive Adhesive Layer)

Pressing at ordinary temperature (23° C.) and a pressure of 3 MPa forthree seconds was conducted a total of hundred times on a sampleheat-peelable pressure-sensitive adhesive sheet having a surface area of2 cm². How far the glue (pressure-sensitive adhesive component) extruded(misregistration) was determined, and the misregistration of theheat-expandable pressure-sensitive adhesive layer was evaluatedaccording to the following criteria. The extrusion herein was an averageof maximum extrusions of the four sides.

Criteria

Good: The extrusion is 0.02 mm or less.

Poor: The extrusion exceeds 0.02 mm.

In the evaluations of the peelability upon heating and themisregistration of the heat-expandable pressure-sensitive adhesivelayer, “Good” means good property, and “Poor” means poor property.

TABLE 1 Misregistration of heat- Shear modulus (Pa) TackinessPeelability expandable 23° C. 80° C. 95° C. (N/20-mm) upon heatingadhesive layer Ex. 1 2.3 × 10⁷ 2 × 10⁶ 5 × 10⁵ 4.2 Good Good (0.01 mm orless) Ex. 2   5 × 10⁷ 4 × 10⁶ 8 × 10⁵ 3.0 Good Good (0.01 mm or less)Com. Ex. 1 2.3 × 10⁷ 2 × 10⁶ 5 × 10⁵ 0.1 or less Good Poor (0.05 mm)Com. Ex. 2   5 × 10⁷ 4 × 10⁶ 8 × 10⁵ 0.1 or less Good Poor (0.03 mm)

Table 1 shows that the heat-peelable pressure-sensitive adhesive sheetsaccording to Examples 1 and 2 can be easily and firmly applied to anadherend at ordinary temperature (room temperature; 23° C.) as withregular pressure-sensitive adhesive tapes.

They have a suitable shear modulus at room temperature and a good shearmodulus at 80° C. and 95° C., and, therefore, can effectively exhibitexcellent elastic force and tackiness. More specifically, they showsubstantially no misregistration (slippage) of the heat-expandablepressure-sensitive adhesive layer even upon pressing under pressure atroom temperature. Of course they can be easily peeled off from theadherend (or processed article) as a result of heating.

The heat-peelable pressure-sensitive adhesive sheets of Examples 1 and 2according to the present invention, if used in processing of adherends,can effectively improve the component precision, enable the adherend tohave a reduced size, and improve yields to thereby improve theproductivity.

INDUSTRIAL APPLICABILITY

As is described above, the heat-peelable pressure-sensitive adhesivesheets according to the present invention can be used aspressure-sensitive adhesive tapes in the production of electroniccomponents and semiconductor components. They can prevent thedeformation of the pressure-sensitive adhesive layer caused bypressurization in the pressing process and can exhibit excellenttackiness and prevent the misregistration (misregistration) of theadherend in the laminating and cutting processes in the production ofelectronic components. They can exhibit excellent tackiness and furtherreduce chipping in the grinding and cutting processes in the productionof semiconductor components. In addition, they can be easily peeled offfrom the processed article and can be easily applied to the adherend atordinary temperature.

Consequently, the heat-peelable pressure-sensitive adhesive sheetsaccording to the present invention, if used in processing of adherends,can effectively improve the component precision, enable the adherend tohave a reduced size, and improve yields to thereby improve theproductivity.

1. A heat-peelable pressure-sensitive adhesive sheet comprising asubstrate; and a heat-expandable pressure-sensitive adhesive layerarranged on or above at least one side of the substrate, theheat-expandable pressure-sensitive adhesive layer containing a foamingagent and having a shear modulus (23° C.) in an unfoamed state of 7×10⁶Pa or more, wherein the adhesive sheet further comprises apressure-sensitive adhesive layer being arranged on or above theheat-expandable pressure-sensitive adhesive layer and having a shearmodulus (23° C.) of less than 7×10⁶ Pa.
 2. The heat-peelablepressure-sensitive adhesive sheet according to claim 1, wherein theheat-expandable pressure-sensitive adhesive layer comprises apressure-sensitive adhesive having a shear modulus (23° C.) after beingcured or dried of 7×10⁶ Pa or more, and wherein the pressure-sensitiveadhesive layer arranged on or above the heat-expandablepressure-sensitive adhesive layer comprises a pressure-sensitiveadhesive having a shear modulus (23° C.) after being cured or dried ofless than 7×10⁶ Pa.
 3. The heat-peelable pressure-sensitive adhesivesheet according to one of claims 1 and 2, wherein the pressure-sensitiveadhesive layer arranged on or above the heat-expandablepressure-sensitive adhesive layer has a thickness of 0.01 to 10 μm. 4.The heat-peelable pressure-sensitive adhesive sheet according to claim1, further comprising an organic rubber-like elastic layer arrangedbetween the substrate and the heat-expandable pressure-sensitiveadhesive layer.
 5. The heat-peelable pressure-sensitive adhesive sheetaccording to claim 1, wherein the heat-expandable pressure-sensitiveadhesive layer has a shear modulus (95° C.) in an unfoamed state of lessthan 7×10⁶ Pa.
 6. The heat-peelable pressure-sensitive adhesive sheetaccording to claim 1, wherein the foaming agent in the heat-expandablepressure-sensitive adhesive layer has a foam initiating temperaturehigher than 80° C.
 7. A method of processing an adherend, comprising thesteps of applying the heat-peelable pressure-sensitive adhesive sheetaccording to claim 1 to the adherend, and subjecting the adherend toprocessing.
 8. The method of processing an adherend according to claim7, wherein the adherend is an article to be an electronic component. 9.The method of processing an adherend according to claim 7, wherein theadherend is an article to be a semiconductor component.
 10. Anelectronic component produced using the method of processing an adherendaccording to claim
 8. 11. A semiconductor component produced using themethod of processing an adherend according to claim 9.